Vapor permeable, liquid impermeable polymeric films are known in the art. One method of making a polymeric film vapor permeable, involves mixing a matrix polymer with a substantial quantity (e.g. 10-70% by weight) of an organic or inorganic particulate filler such as, for example, calcium carbonate, and extruding a film from the blend. The matrix polymer may include a polyolefin, such as polyethylene or polypropylene, or various olefin copolymers. The film may be a monolayer film, a multilayer film which contains the filled layer as a primary layer, or a multilayer film having more than one filled layer.
Then, the film is heated and stretched, causing voids to form in the areas surrounding the filler particles. The voided film is characterized by thin polymer membranes and/or fine pore networks which permit the molecular diffusion of water vapor through the film, but which block the passage of liquids. In essence, a tortuous path is created from one film surface to the other which permits transfer of vapors but not liquids.
Breathable films are employed in backsheets, for example as a backsheet component laminated to a nonwoven web and/or other layers, in many of today's personal care absorbent articles. Diapers are one example. Filled, stretched polyolefin films provide good water vapor transmission, making the diapers more comfortable to the wearer. As a result, the relative humidity and temperature within the diaper or other product can be reduced by using breathable films and laminates. Despite this, breathable films have the disadvantage of being cold and clammy to the touch, because moisture which passes through the films condenses readily on the outer surface. Accordingly, when nonwoven webs are laminated to the films, the laminates are placed with the film on the inside (diaper facing side) and the nonwoven web on the outside of the laminate.
Even with the use of nonwoven layers, a wet feeling may develop as the condensed moisture from the film penetrates the adjacent nonwoven layer. There is a need or desire for a breathable film useful in a backsheet for absorbent articles which exhibits increased barrier when the film surface gets wet.
Breathable films are also used in surgical gowns. Again, the objective is to provide good water vapor transmission and make the gowns comfortable to the wearer. However, if a gown is too breathable, it may be less effective in providing barrier when exposed to an insult from a potentially contaminated liquid, such as blood. For surgical gowns, there is a need or desire for a breathable film which exhibits increased barrier to pressure induced penetration when exposed to a liquid insult.